1. Field of the Invention
The present invention relates to electronic circuits and, in particular, to an operational transconductance amplifier which can source more current than presently available operational amplifiers.
2. Discussion of the Prior Art
The operational amplifier of the present invention improves on the shortcomings of the two conventional operational amplifier structures which allow rail to rail output swings: the classical two stage amplifier and the classical operational transconductance amplifier.
A schematic of a classical two stage amplifier is provided in FIG. 1 and is described by Gray and Meyer, "Analysis and Design of Analog Integrated Circuits," p. 742, FIG. 12.32 (Wiley). The disadvantage of this type of circuit is that, while it can sink substantial current, it cannot source current in excess of the output stage quiescent current. Either a high quiescent current or low source capability must be accepted for any particular application.
A schematic of a classical operational transductance amplifier is provided in FIG. 2 and is described by Tsividis and Antognetti, "Design of MOS VLSI Circuits for Telecommunications," p. 129, FIG. 5.11 (Prentice Hall). This type of circuit exhibits relatively low gain since it is single staged. Furthermore, it is unable to source or sink more than twice the output stage quiescent current.